Squats build tremendous mass and power in the lower body, especially the thighs.
Squats are one of the best yet most grueling mass-building exercises for the
entire lower body.
They
really develop all four heads of the quadriceps. A
lot of people shy away from this exercise because it can be painful and nauseating. However nothing produces more dramatic results!

Implementation: (A) With the barbell on a rack, walk
under the weight so it rests across the back of your shoulders, grip the bar to
balance it, stand up straight to lift the barbell off the rack, and step back.

(B) Have your head up and back straight, bend your knees and lower yourself
until your thighs are parallel with the ground. Now that your parallel, drive
yourself back up to the starting position. It is important to go parallel in
this movement, especially when you are new to this exercise, so that you develop
strength along the entire range of motion. If you don't go low enough in the
beginning, you can easily hurt yourself later when using heavier weight. Foot
position in this exercise establishes which area of the thighs you work the most
while doing Squats: A wider stance works the inside of the thighs to a greater
extent, when in a narrower stance you tend to work the outside more; if your
toes are pointed out it hits the inside of the thighs. The normal position for greatest power is usually feet shoulder-width apart, with toes
turned just slightly outward.